Fillerbunny was, unsurprisingly, easily distracted from time to time. Quite often, in fact. Plus, being a rabbit, albeit a heavily modified one, his sense of time was not quite what most humans experienced, and so the days tended to run together, and his sense of the passage of time was often confused. The needles in the brainmeats hadn't helped with that either.
First, there was the pretty but nervous lady who he sorted into Slytherin. He had wandered around for some time afterwards, trying to figure out what she was afraid of. Then he'd found out he was nominated to be a Prefect! Whatever that meant! And then Mister Bignose needed attending, and Fillerbunny felt bad, because he knew he'd been ignoring his aardvark friend in favor of looking after Miss River. And then there was the Prefect Debate, which was weird and scary ... and now Fillerbunny realised he hadn't seen Miss River in ... some time. And he definitely hadn't seen Doctor Stephen in quite a while.
So after making sure that Mister Bignose was comfortable, he headed out to look for Stephen first, planning to seek him first in his office and then in his rooms, and then (he thought) they would go see Miss River together.
((Hope this works as an RP kickoff seed ... wanted to try and fit it into the continuity with the other stuff that's been demanding FB's attention.))